A. Yes, you can buy health insurance from the state exchange outside of open enrollment if you experience some of the life changes, such as losing employer health insurance coverage (even you qualify for COBRA), having a baby, move to a new area, etc.
To qualify for health insurance subsidy, your income must be below 4 times of Federal poverty level (about $62,000 for couples), since you don't know your actual income yet, you can estimate it. When you know the actual amount you earn, you could either get a refund or pay some of the subsidy back. You can adjust the numbers during the year by contacting the exchange.